1. Field of the Invention
The present invention relates to a sublimation transfer type thermal printer and ink ribbon used by the printer, and more particularly relates to the technique of stabilizing the print quality by making a precise control of the print density.
2. Description of the Prior Art
The sublimation transfer type thermal printer has an ability to achieve smooth and natural gradation expression, and is characterized by its excellent expressiveness, high print quality and natural image reproducibility. In this view, it is frequently used for the special purpose which requires printing of high quality and high fidelity, such as an output of printed matter for the correction, medical printings such as CT-scanner or radiograph, or color samples of products in the apparel industry or other industry. In such cases, simply printing the original image data does not satisfy the requirement of special printing quality. Therefore, in such cases, the original image data is corrected to compensate for the variation of the ink ribbon characteristics, and the corrected image data is printed.
The variation in characteristic of the ink ribbons result in the problem that an appropriate normal gradation with respect to the print density cannot be reproduced, even if the printing condition of the thermal printer is uniform. Particularly, in the color printing, all colors are reproduced by superposing the images of three primary colors (Yellow, Magenta and Cyan) or four primary colors (Y, M, C, and Black) by using the ink ribbons of those colors. Therefore, if the normal gradation reproduction is not ensured in at least one color, the color balance is broken and high fidelity reproduction may not be achieved. In this view, the gradation correction is performed. Conventionally, the manufacturer of the ink ribbon performs test printing for respective lot of the ink ribbons, measures the print density of the test printing to calculate the correction data, and sells the ink ribbon product with the correction data sheet or the like attached. The user of the ink ribbon inputs the correction data to his printing system or image processing system via keyboard or the like to make the appropriate gradation correction, before starting the printing.
However, in such a case, the user needs to input the correction data by manual operation every time when he exchange the ink ribbon, and it is very time-consuming and troublesome. Moreover, there is relatively large possibility of erroneously inputting the correction data because many correction values should be inputted.